The ototoxic effects of ethyl benzene in rats

Exposure to organic solvents has been shown to be ototoxic in animals and t here is evidence that these solvents can induce hearing loss in humans. In this study, the effects of inhalation of the possibly ototoxic solvent ethy l benzene on the cochlear function and morphology were evaluated using thre e complementary techniques: (1) reflex modification audiometry (RMA), (2) e lectrocochleography and (3) histological examination of the cochleas. Rats were exposed to either ethyl benzene (800 ppm, 8 h/day for 5 days) or to co ntrol conditions. The RMA threshold increased significantly by about 25 dB, 1 and 4 weeks after the exposure, irrespective of the stimulus frequency t ested (4-24 kHz). Electrocochleography was performed between 8 and 11 weeks after exposure to the organic solvent. The threshold for the compound acti on potential increased significantly by 10-30 dB at all frequencies tested (1-24 kHz). Histological examination of the cochlea showed outer hair cell (OHC) loss, especially in the upper basal and lower middle turns (correspon ding to the mid-frequency region) to an extent of 65%. We conclude that exp osure to 800 ppm ethyl benzene for 8 h/day during 5 days induces hearing lo ss in rats due to OHC loss. (C) 1999 Elsevier Science B.V. All rights reser ved.